For many decades, half duplex two-way radio networks have provided reliable and convenient communications using limited shared radio resources. For example, “walkie-talkie” and citizens band (CB) radio networks have enabled users to maintain direct communication channels with other users over extended periods of time. The push-to-talk (PTT) and “instant on” features of half duplex radio devices provide desirable modes of wireless communication for users such as truckers, construction and industrial site personnel, military personnel, taxi dispatchers, police and fire personnel and numerous others. Many modern communication systems designed for public safety use group communications, which allow two or more participants to exchange voice, video, and other data. A floor control mechanism then dictates which device in the network is permitted to source media at a given time.
Project 25 (P25) concerns a set of standards for digital radio communications for use by various emergency response teams. P25 was established to address the need for common digital public safety radio communications standards, including PTT communications standards. The P25 suite of standards involves digital land mobile radio (LMR) services commonly used by police and fire departments, and other public safety organizations. The P25 standards define numerous internet protocol (IP) network-to-network interfaces, which provide interoperability between P25 systems. For example, these interfaces include an ISSI for PTT which was published by the Telecommunications Industry Association (TIA) in the TIA.102-BACA documents. The ISSI provides network connectivity between P25 networks and enables network administrators to connect to other local, regional, state, or federal networks. A radio frequency subsystem (RFSS) contains a PTT server which is used during a P25 PTT session, and the ISSI enables communications between PTT servers in different RFSSs. The P25 standards governing the ISSI also define which RFSS controls a PTT session, and how a controlling RFSS maintains floor control during a PTT session.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.